In the last few years, wind power production has become a very important energy source. Cumulative wind power worldwide is increasing remarkably and so is its share in the mix of energy production. Consequently, generation of energy from wind farms should contribute to the stability of the electrical network which is directly related to the generation or consumption of reactive power. Thus, it is necessary to perform a reactive power control in the wind farms.
However, reactive power management is often not considered as a key player for keeping the electrical network stable. Generally, reactive power production plays a secondary role in wind farm power production strategy and is usually based on the local grid voltage measurement.
Several patents have been filed concerning reactive power control in wind farms. For instance, U.S. Pat. No. 6,965,174 describes a method for operating a wind turbine in which the current phase angle is changed in response to at least one voltage measured in the grid. In addition, US 2005/0046196 also describes a method in which a reactive power setpoint, mainly generated as a consequence of a voltage measurement, is provided to the wind turbine generators. Said setpoint is achieved by controlling the wind turbine voltage.
As stated above, wind energy generation and, particularly, reactive power control should take an active part in the stability and quality of the electrical grid. Thus, reactive power compensation may have the following aims:                Fulfillment of electrical network demands.        Keeping a reactive power reserve in order to support grid contingencies.        
These objectives may even lead to giving priority to reactive power over active power production depending on network conditions.
Another aspect of prior methods is that reactive power compensation is managed by the wind turbines without balancing the demanded control effort, in which the control effort is the ratio of reactive power production to the instantaneous reactive power capacity of each wind turbine. That is, reactive power compensation is carried out by all the wind turbines without an optimization strategy, probably resulting in some of them suffering from higher electrical stress and wear while others might remain below their capabilities.